1. Field of the Invention
The present invention relates mainly to a heater used in heating a wafer, a wafer heating apparatus and a method for manufacturing the heater.
2. Description of the Related Art
In a manufacturing process of semiconductor devices, a heater is used to heat a semiconductor wafer (hereinafter referred to simply as a wafer) during formation of thin semiconductor film, etching, baking of resist film and other steps.
For such heating purposes, for example, Patent Document 1, Patent Document 2 and Patent Document 3 disclose wafer heating apparatus as shown in FIG. 16.
A heater 771 comprises a plate-shaped ceramic member 772 and a metal casing 779 as major components, and is constituted by securing the plate-shaped ceramic member 772 made of a ceramic material of nitride or carbide on an opening of the bottomed metal casing 779, that is made of a metal such as aluminum, via an insulating contact member 774 made of a resin by means of bolts 780. The heater 771 uses the top surface of the plate-shaped ceramic member 772 as a heating surface 773 whereon a wafer W is to be mounted, so that the wafer W is heated by a resistive heating member 775 that is formed, for example, in concentric configuration as shown in FIG. 20, on the bottom surface of the plate-shaped ceramic member 772.
Power terminals 777 are connected by brazing to power feeder sections of the resistive heating member 775, with the power terminals 777 electrically connected to lead wires 778 that are passed through wiring holes 776 provided at a bottom 779a of the metal casing 779.
In order to form a uniform film over the entire surface of the wafer W or cause a resist film to react uniformly in heating reaction by using the heater 771, it is important to make uniform temperature distribution over the wafer. Accordingly, various measures have been employed as described below to keep the temperature difference across the wafer surface small.
One of the measures is to divide the resistive heating member 775 and independently control the temperatures of the divided sections.
Patent Document 4 discloses a heater that has a plurality of resistive heating member blocks. The resistive heating member of this heater is radially divided into four equal sections of fan-shaped block as shown in FIG. 17. A heater such as shown in FIG. 18 is also known that comprises four blocks of resistive heating member located along the periphery and a circular block of resistive heating member located at the center.
Patent Document 5 discloses a heater comprising a resistive heating member that is divided into identical rectangular regions 711 through 718 that can be controlled either independently or in groups each consisting of a plurality of regions, as shown in FIG. 19. In this heater, as shown in FIG. 19, four regions 715 through 718, among the regions 711 through 718, are located at positions that correspond to the arcs formed by dividing the peripheral portion of the wafer into four equal parts, and other four regions 711 through 714 are disposed inside of the four regions 715 through 718 in parallel thereto.
As to configuration of the resistive heating member, such a heater 500 (Patent Document 6) that comprises a plurality of resistive heatin members of which one located at the outermost position is formed in a sine curve, and heater 500 having outermost resistive heating member 750 formed in rectangular shape (Patent Document 7 and Patent Document 8) is also disclosed (FIGS. 21, 22, 23). In these heaters, a power feeder section 760 is disposed adjacent to the resistive heating member.
Patent Document 8 discloses a heater having a spiral-shaped resistive heating member.
Patent Document 9 discloses a heater where wafer W support pins (not shown) are provided on a mount surface 773 is provided so as to lift the wafer W from the mount surface 773 by a small distance, in order to achieve uniform temperature distribution over the wafer.
Patent Document 10 discloses a heater where a wall is provided along the periphery of the plate-shaped ceramic member 772 to surround the wafer W, so as to prevent the wafer W from moving laterally.
Patent Document 11 discloses a heater where a protrusion that engages with the wafer W is formed along the periphery of the plate-shaped ceramic member 772, and a multitude of projections that contact with the wafer W are formed inside of the protrusion, in order to achieve uniform temperature distribution.
Patent Document 12 discloses a heater where guide pins that locate the wafer W are provided around the plate-shaped ceramic member, thereby to achieve uniform temperature distribution over the wafer W.
Patent Document 13 discloses a heater where temperature distribution over the wafer W can be controlled by adjusting the height of support pins of the wafer W. A heater having guide pins engaged with the support pins is also disclosed.
Patent Document 14, Patent Document 15 and Patent Document 16 also disclose heater 850 made of ceramics where a coil-shaped resistive heating member 853 is embedded as shown in FIG. 24. The heater 850 consists of a plate-shaped ceramic member 851 made of a nitride ceramic material such as silicon nitride or aluminum nitride in which a coil-shaped resistive heating member 853 formed in spiral configuration is embedded, while the power feeder terminals 855 are connected to both ends of the resistive heating member 853. In order to decrease the temperature difference across the wafer surface, such measures are disclosed as increasing the density of the resistive heating member 853 in a region of 10% of the mount surface on the outside, restricting the variation in the number of windings per unit length of the coil-shaped resistive heating member 853 and 3-dimensional arrangement of the resistive heating member 853.
Patent Document 17 and Patent Document 18 also describe attempts to decrease the temperature difference across the wafer surface by connecting and embedding a resistive heating member having different coil diameter, or by providing a swelling portion at a turn-back portion of the resistive heating member.
Moreover, in a CVD film forming process, for example, such a wafer holding member is employed that supports a ceramic heater comprising a plate-shaped ceramic member by means of a cylindrical support member made of ceramics. Such a heater 850 made of ceramics is also known as one principal surface of the plate-shaped ceramic member 851 having resistive heating members 853, 854 embedded therein is used as mount surface 851a and a cylindrical support member 860 made of ceramics is joined onto the other principal surface, as shown in FIG. 25. In the heater 850, the power terminals 856, 857 are connected by brazing to the terminals of the resistive heating members 853, 854, and power terminals 856, 857 are lead through inside of the cylindrical support member 860 to the outside for connection.
In recent years, increasing number of semiconductor devices are manufactured with circuits having line width of 90 nm or 45 nm. Manufacturing such semiconductor devices requires a heater that can heat a wafer with more uniform temperature distribution.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2001-203156
[Patent Document 2]
Japanese Unexamined Patent Publication No. 2001-313249
[Patent Document 3]
Japanese Unexamined Patent Publication No. 2002-76102
[Patent Document 4]
Japanese Unexamined Patent Publication No. 11-121385
[Patent Document 5]
Japanese Unexamined Patent Publication No. 11-354528
[Patent Document 6]
Japanese Unexamined Patent Publication No. 2001-6852
[Patent Document 7]
Japanese Unexamined Patent Publication No. 2001-223257
[Patent Document 8]
Japanese Unexamined Patent Publication No. 2001-257200
[Patent Document 9]
Japanese Unexamined Patent Publication No. 10-223642
[Patent Document 10]
Japanese Unexamined Patent Publication No. 10-229114
[Patent Document 11]
Japanese Unexamined Patent Publication No. 2002-237375
[Patent Document 12]
Japanese Unexamined Patent Publication No. 2002-184683
[Patent Document 13]
Japanese Unexamined Patent Publication No. 2001-68407
[Patent Document 14]
Japanese Unexamined Patent Publication No. 4-101381
[Patent Document 15]
Japanese Unexamined Patent Publication No. 7-220862
[Patent Document 16]
Japanese Unexamined Patent Publication No. 7-65935
[Patent Document 17]
Japanese Unexamined Patent Publication No. 2004-6242
[Patent Document 18]
Japanese Unexamined Patent Publication No. 2004-111107
[Patent Document 19]
Japanese Unexamined Patent Publication No. 11-339939
[Patent Document 20]
Japanese Unexamined Patent Publication No. 2001-102157
[Patent Document 21]
Japanese Unexamined Patent Publication No. 2002-170655
There has been a demand for a heater that can heat a wafer with more uniform temperature distribution with a simpler structure, since it is difficult to achieve uniform temperature distribution with the conventional heater and it is necessary to carry out very complex and delicate control procedure to achieve a uniform temperature distribution.
In the case of the technology of chemically amplified resist that is being employed along with the trend toward smaller circuit line width of the semiconductor devices, emphasis is placed not only on the uniform temperature distribution over the wafer, but also on the temperature changes throughout the period from the time when the wafer is set in a heat treatment apparatus to the time when the heat treatment is completed and the wafer is taken out. Thus it is desired to stabilize the wafer temperature in uniform temperature distribution with about 60 seconds after placing the wafer on a heater, but the conventional heater cannot satisfy this requirement because it takes a long period of time to stabilize the temperature.
There has also been such a problem that a heater comprising a coil-shaped resistive heating member embedded therein has a tendency of the density of the heating member changing significantly between the outside and inside at a bending portion of the resistive heating member, which makes it difficult to decrease the radius of curvature. Accordingly, the methods described in Patent Document 17 and Patent Document 18 require it to connect the resistive heating members of different coil diameters within the plate-shaped ceramic member, or to form a swelling portion at a turn-back section of the resistive heating member. This results in a complex process that is not suitable for volume production, and it is very difficult to mass-produce products with stabilized quality and high level in the yield of production.
In addition, there has been such a problem that the heater having the cylindrical support member attached thereto allows heat to dissipate through the cylindrical support member, thus resulting in significant temperature difference across the wafer surface.
To counter this problem, Patent Document 19 discloses a heater having increased resistance density on the inside of the cylindrical support member 860 so as to keep the temperature difference across the wafer surface small even when the temperature is raised quickly and prevent the plate-shaped ceramic member 851 from breaking.
Patent Document 20 discloses a heater made of ceramics having a cylindrical support member attached thereto wherein temperature difference across the surface is decreased to prevent breakage, by increasing the resistance of a middle portion and an independent resistive heating member 854 is embedded at a position near the joint surface of the support member 860. Furthermore, Patent Document 21 discloses a heater having a resistive heating member embedded therein so as to heat the cylindrical support member 860.
Recently, it has been called for to decrease the time taken to raise the temperature to a very short period. However, there is a possibility that the heater made of ceramics having the coil-shaped resistive heating member breaks when heated at a high rate. Particularly, heaters made of ceramics having cylindrical support members attached thereto designed for increasing wafer size of 300 mm in diameter were often broken due to the high thermal stress generated by quick heating.